Mother birds deposit variable amounts of antioxidants into egg yolks, and it has long been theorized that females invest more in offspring sired by better quality males. However, a study from the November/December 2006 issue of Physiological and Biochemical Zoology shows that even ugly birds get their day. Providing new insight into the strategic basis behind resource allocation in eggs, the researchers found that female house finches deposit significantly more antioxidants, which protect the embryo during the developmental process, into eggs sired by less attractive fathers.
"For female birds, an important aspect of parental investment is the resources allocated to eggs," writes Dr. Kristen J. Navara (Auburn University and Ohio State University) and her coauthors. "The resources available to any female for reproduction and self-maintenance will be finite and she will inevitably be faced with decisions regarding how much resource to invest in each egg in each clutch she lays."
Male house finches display nutrition-linked plumage ranging in color from bright red to drab yellow. The researchers found that eggs sired by unattractive males (those with less brilliant feathers) had more total antioxidants, including 2.5 times the vitamin E levels, than eggs sired by males with redder, more saturated plumage. Thus, they explain, the deposition of more nutrients could represent compensation for the disadvantages experienced by an offspring from a lower quality male, allowing females to supersede limitations of a suboptimal pairing on her own reproductive success.
"For house finches, a species in which individuals are short-lived [and] present a high risk of death, a focus on the immediate reproductive attempts may be the only viable strategy," write the researchers. "By depositing antioxidants in a compensatory manner, females can maximize the reproductive output from the current nesting effort."
Since 1928, Physiological and Biochemical Zoology has presented original, current research in environmental, adaptational, and comparative physiology and biochemistry.
Kristen J. Navara, Alexander V. Badyaev, Mary T. Mendonca, and Geoffrey E. Hill. "Yolk antioxidants vary with male attractiveness and female condition in the house finch (Carpodacus mexicanus)." Physiological and Biochemical Zoology 79:6.
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